This invention relates to hydrocarbon conversion catalysts, and particularly to those utilized to catalyze the reaction of hydrogen with organic compounds containing nitrogen and/or sulfur so as to yield a denitrified and/or desulfurized product. More particularly, the invention is directed to catalysts, and a method for preparing catalysts, useful for the hydrodesulfurization and/or hydrodenitrogenation of hydrocarbon liquids. The invention is especially directed to catalysts of high hydrodenitrogenation activity.
In the refining of liquid hydrocarbons derived from mineral oils and other sources, it is often necessary to subject the liquid hydrocarbon or fraction thereof to hydrotreating. Hydrotreating is a process for reducing the concentration of nitrogen and sulfur components in a hydrocarbon feedstock so that, when the product hydrocarbon is eventually combusted, less SO.sub.2 and NO will form, and hence present less of a pollution problem. In addition, it is often desirable to remove nitrogen from such feedstocks in order to protect hydrocracking catalysts and the like which deactivate in the presence of nitrogen.
In general, hydrotreating is accomplished by contacting the feedstock containing nitrogen and/or sulfur with a catalyst in the presence of hydrogen and under conditions, including elevated temperature and pressure, such that the sulfur components are converted to H.sub.2 S and the nitrogen components to NH.sub.3, both of which are separated from the desulfurized and denitrogenated liquid product.
A typical hydrotreating catalyst comprises particles containing a Group VIII active metal component and a Group VIB active metal component supported on a refractory oxide such as alumina. Oftentimes, phosphorus components are also present in the catalyst to improve its activity by increasing its acidity. One catalyst which has been successfully employed on a commercial basis consists essentially of molybdenum, nickel, and phosphorus components supported on gamma alumina. A typical preparation procedure for such a catalyst is as follows: particles of hydrated alumina are firstly formed into a desired size and shape by extruding the hydrated alumina through a die having circular or clover leaf-shaped openings therein and cutting the extruded matter into particles (or extrudates) of 1/16-1/2 inch lengths. After calcining at a temperature of about 1150.degree.-1250.degree. F., the resulting gamma alumina extrudates are in a condition to be contacted with an impregnating solution comprising dissolved salts of molybdenum and nickel in phosphoric acid. The impregnated extrudates (or composites) are then subjected to a final calcination at a temperature around 900.degree. F. to convert the impregnated metals to their oxide forms. Subsequent conversion of the oxides to sulfides, as by contact at elevated temperatures with a hydrogen-hydrogen sulfide mixture or a hydrocarbon liquid containing organic sulfur compounds, produces a catalyst of high activity for simultaneous hydrodesulfurization and hydrodenitrogenation under conventional hydrotreating conditions. Such catalysts are especially useful where high denitrogenation activity is required.
Despite the high desulfurization and denitrogenation activity of the catalysts of the prior art, catalysts of yet higher activities are still being sought. The higher the activity of the catalyst, the more mild the conditions required to obtain a product of given sulfur and nitrogen content from a feedstock of given sulfur and nitrogen content, and the more mild the conditions, the less the amount of fuel that is consumed to achieve the desired product. Also, when more mild conditions are used, the catalyst life is extended due to lower coke formation.
In U.S. Pat. No. 2,813,837 issued to Holden, a method is taught for preparing a metals-supported catalyst, such as those comprising cobalt and molybdenum on alumina, wherein the support is calcined and then hydrated prior to impregnation with the desired active metals. The data in this patent, however, reveal that catalysts prepared by this method exhibit only marginal improvement in both desulfurization and denitrogenation activity in comparison to catalysts of similar composition but prepared without a hydrated alumina support. Accordingly, it is a major object of this invention to utilize hydrated alumina supports to prepare hydrotreating catalysts of dramatically improved denitrogenation and desulfurization activity in comparison to other catalysts of similar or identical composition. Another object is to provide a method for preparing such catalysts, and yet another object is to provide a method for using such catalysts for denitrogenating and/or desulfurizing hydrocarbon feedstocks containing detrimental nitrogen and/or sulfur compounds. A further object is to provide a hydrotreating catalyst of superior overall hydrodenitrogenation and/or hydrodesulfurization activity. These and other objects and advantages will become apparent to those skilled in the relevant art in view of the following description of the invention.